Electromagnetic Confinement via Spin–Orbit Interaction in Anisotropic Dielectrics

Alberucci, Alessandro; Jisha, Chandroth P.; Marrucci, Lorenzo; Assanto, Gaetano

doi:10.1021/acsphotonics.6b00700

Cited by 27 publications

(29 citation statements)

References 29 publications

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“…This means that the polarization of the field will always vary while evolving along z, in turn leading to the occurrence of a transversely-varying PBP, whenever θ is not uniform. In accordance with the former statement, in the case of linear birefringence it is well known that the wavefront is strongly affected by the PBP, both for short [12,16,19] or long propagation [24,27] with respect to the Rayleigh distance. Light propagation changes drastically in the presence of circular birefringence, that is, 2D = ( 1 , −iγ; iγ, 2 ), where γ is the modulus of the gyration vector.…”

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confidence: 69%

“…[5,6,8] where geometric optics is used, here the wave behavior of the electromagnetic radiation is accounted for. Differently from the case of linear birefringence [24], we demonstrate that in optically active media the two circular polarizations see a photonic potential reversed in sign, yielding polarizationdependent guiding and SHE. Let us consider the monochromatic propagation of an electromagnetic field [amplitude ∝ exp (−iωt)] in an inhomogeneous anisotropic material.…”

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confidence: 67%

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Spin-orbit interactions in optically active materials

Jisha

Alberucci

2017

Opt. Lett.

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We investigate the inherent influence of light polarization on the intensity distribution in anisotropic media undergoing a local inhomogeneous rotation of the principal axes. Whereas in general such configuration implies a complicated interaction between geometric and dynamic phase, we show that, in a medium showing an inhomogeneous circular birefringence, the geometric phase vanishes. Due to the spin-orbit interaction, the two circular polarizations perceive reversed spatial distribution of the dynamic phase. Based upon this effect, polarization-selective lens, waveguides and beam deflectors are proposed.The simplest approaches in wave optics model light as a scalar wave, an approximation valid only for paraxial beams propagating in isotropic homogeneous media [1]. The electromagnetic nature of light implies that photons have spin, appearing in the Maxwell's equations as the field polarization. Nonetheless, in case of paraxial waves propagating in isotropic materials, the spatial degree of freedom (i.e., the field distribution) is independent of the polarization. This is not rigorously true due to the vectorial nature of the Maxwell's equation, leading to a socalled classical entanglement [2,3]. The discrepancies between the two approaches are significant, for example, in case of non-paraxial beams leading to polarizationdependent focusing [4], or for polarization-dependent trajectory of light in inhomogeneous materials, the so called optical Magnus effect, aka spin Hall effect (SHE) of light [5][6][7][8].In this context, the investigation of spin-orbit interaction is rapidly becoming a central topic in optics [9]. Photons have been demonstrated to be a unique tool for the investigation of basic quantum field theory [10,11]. On the other hand, spin-orbit interaction paves the way to a new family of ultra-thin photonic devices, including gratings [12] In anisotropic media another type of geometric phase arises, the Pancharatnam-Berry phase (PBP). PBP appears in the presence of a rotation of the beam polarization for a fixed wave-vector. Noteworthy, in anisotropic materials spin-orbit effects, such as birefringence or spatial walk-off, are observed even for plane waves due to the * alessandro.alberucci@gmail.com dependency on polarization of the light-matter interaction [21]. Nonetheless, the presence of PBP in anisotropic media widens the spectrum of the observable spin-orbit effects [12,13,16], including the nonlinear case [22,23]. The PBP affects the wavefront, and thus light propagation, when the anisotropic medium is inhomogeneous and showing a point-wise rotation of the principal axes across the intensity profile. In this Letter we first analyze light propagation in inhomogeneously rotated materials considering the trade-off between the PBP and diffraction. We show that PBP vanishes if the material is optically active, the field propagation then being affected by dynamic phase alone. Unlike Refs. [5,6,8] where geometric optics is used, here the wave behavior of the electromagnetic radiation is accounted fo...

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confidence: 67%

Spin-orbit interactions in optically active materials

Jisha

Alberucci

2017

Opt. Lett.

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“…In a recent Letter we showed that light propagates under the influence of an effective photonic potential, leading to leaky guided modes for bell-shaped distributions of the optic axis rotation [35] (Fig. 1).…”

Section: Introductionmentioning

confidence: 93%

“…In Section III we generalize to the three-dimensional case the paraxial equations governing light propagation found in Ref. [35] to the case of long (with respect to the Rayleigh length) samples. We also Gaussian distribution of the rotation angle θ on the plane xy when maximum rotation is 90 • : the arrows correspond to the local optic axis (i.e., the extraordinary axis), superposed to the spatial distribution of θ represented as a color map.…”

Section: Introductionmentioning

confidence: 96%

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Interplay between diffraction and the Pancharatnam-Berry phase in inhomogeneously twisted anisotropic media

et al. 2017

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We discuss the propagation of an electromagnetic field in an inhomogeneously anisotropic material where the optic axis is rotated in the transverse plane but is invariant along the propagation direction. In such a configuration, the evolution of an electromagnetic wave packet is governed by the Pancharatnam-Berry phase (PBP), which is responsible for the appearance of an effective photonic potential. In a recent paper [ACS Photon. 3, 2249 (2016)] we demonstrated that the effective potential supports transverse confinement. Here we find the profile of the quasimodes and show that the photonic potential arises from the Kapitza effect of light. The theoretical results are confirmed by numerical simulations, accounting for the medium birefringence. Finally, we analyze in detail a configuration able to support nonleaky guided modes

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Geometric Phase in Optics: From Wavefront Manipulation to Waveguiding

Jisha

Nolte

Alberucci

2021

Laser & Photonics Reviews

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Geometric phase is a unifying and central concept in physics, including optics. As a matter of fact, optics played a pivotal role from the inception of this new paradigm, as some of the first experimental demonstrations have been carried out in optics. A specific type of geometric phase was first introduced by Pancharatnam while investigating interference effects between different polarizations. This specific type of geometric phase, nowadays called the Pancharatnam–Berry phase, is related to the variation of light polarization, encompassing exotic properties when compared with the dynamic phase associated with the optical path. The most widespread manifestation of the Pancharatnam–Berry phase occurs in the presence of a twisted anisotropic material, yielding a point‐wise phase modulation proportional to the local rotation angle of the material. Here the basic mechanism behind the Pancharatnam–Berry phase is discussed. The various applications of this relatively original concept in photonics are then reviewed, presenting both the most important results and manufactured devices reported in literature. The interplay between geometric phase and diffraction occurring in bulk structures is discussed in detail. In the latter case it is shown how geometric phase can be harnessed to generate a new kind of optical waveguide without the necessity of any index gradient.

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Electromagnetic Confinement via Spin–Orbit Interaction in Anisotropic Dielectrics

Cited by 27 publications

References 29 publications

Spin-orbit interactions in optically active materials

Spin-orbit interactions in optically active materials

Interplay between diffraction and the Pancharatnam-Berry phase in inhomogeneously twisted anisotropic media

Geometric Phase in Optics: From Wavefront Manipulation to Waveguiding

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